Patent GB-795876-A (GB)
Title: Improvements in electrical communication systems
IPC: H04M1/65
Filed: 1955-05-25
Abstract: 795,876. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. May 25, 1955 [May 27, 1954], No. 15076/55. Class 40 (4). Calls to privileged subscribers are answered in their absence by an attendant at a central position. The number of communication channels to the attendant's position is less than the number of lines on which this service is provided and means responsive to a called condition on a line transmit signals to identify the line and allot a free channel to the answering position. General description, Figs. 1 and 2. Each subscriber's line 700 provided with answering service has an auxiliary line circuit 7AUX00 and is given a 2-digit number for identifying the line in the answering service equipment. The corresponding jack and lamp in the answering bureau are similarly designated. The units digit of a called subscriber is identified by units identifier 500 which operates the corresponding select magnets of all the cross-bar switches comprising the trunk connector 900 and tens identifier connector 1300. All the hold magnets in the tens identifier connector 1300 then operate to connect all the subscribers' lines having the appropriate units digit to the tens identifier 1500, which identifies the tens digit to operate one of the controllers 1000 or 1400 through controller connector 1100. The selected controller is connected to start circuit 800 which operates trunk allotter 1700 to allot one of the trunks 16T1-16T4 for answering the call. After a predetermined time the connection from the subscriber's auxiliary line circuit to the trunk is broken. This cycle of operations is repeated during each ringing cycle. The allotted controller, say 1000, applies a potential over trunk 16T1, trunk 22T1, and controller connector 2300 to one of controllers 2700 or 2900, say the former. When the allotted controller 2700 is ready the controller 1000 pulses the units digit to controller 2700 over conductor 16S2 and the ring lead 16TR1 of trunk 16T1, irrespective of whether this trunk is busy and irrespective of the trunk allotted by allotter 1700. During the registration of the units digit controller 2700 operates one of the indicator allotters 2800 or 2901 and prepares indicator connectors 2003-4 and 2101-2 and trunk connector 1900T. The selected indicator allotter, say 2800, allots one of four indicator circuits, say 26IND 1 corresponding to one of the indicator connectors 2101. Controllers 1000 and 2700 transfer the signalling path from ring lead 16TR1 for the units digit to the ring leads of the second trunks 16T2, 22T2 for the tens digit. Controller 2700 uses the tens digit to operate indicator circuit 26IND1 to light the lamp corresponding to the called subscriber. Controller 2700 also operates trunk connector 1900T to provide a connection between the appropriate answer jack and the trunk 22T1 associated with the allotted trunk 16T1. If the attendant does not answer, allotter 2800 releases 2101 and 26IND1 after a predetermined time. When the attendant answers the connection is locked in, the ringing current is tripped, the indicator connector 2101 and indicator circuit 26IND1 are released, and the timing sequences of allotters 1700-2800 are halted. At the end of conversation the attendant disconnects from the switchboard to release the remaining equipment. Detailed description. Fig. 30 shows the arrangement of the component circuits, those figures not used in the Abridgment being enclosed in parentheses. Detecting called condition. Ringing current operates auxiliary line circuit, say 7AUX91, associated with the called subscriber's line, to ionize gas tube 7GT91 and energize ring-up relay 7RU91. Party line arrangements. Some of the gas tubes may have cathodes and starting anodes reversed to distinguish between party lines and individual lines, and in some cases ringing may be effected over the tip lead instead of the ring lead. Units and tens identification. Ring-up relay 7RU91 extinguishes tube 7GT91 and operates the corresponding units relay 5U1 and lock-out relay 5L01 to indicate that the units digit is 1. 7RU91 also operates off-normal relay 8C in the start circuit 800 to initiate a timing operation. 7RU91 energizes 8RMA to start up ringing brush monitor circuit 8RBM which is arranged so that it will not respond more than once in each ringing cycle. 8RMA energizes one of three brush relays 8BR1-8BR3 which holds up and maintains any operated lock-out relay 5L00-5L09 during the 2-second ringing period, after which the brush relay and any operated lock-out relay restore. 5U1 also lights a lamp 4UIL1 (not shown) in an indicator circuit. The operated lock-out relay 5LO1 disables the gas tubes and ring-up relays associated with auxiliary circuits having the same units digit. The selected units relay 5U1 energizes the corresponding select magnets 9SM1 in trunk connector 900 and 13SM1 in tens identifier connector 1300. Operation of select magnet 13SM1 energizes hold magnets 13H8, 13H9 to connect those auxiliary line circuits with a units designation 1 over leads 13S01-13S91 to tens identifier relays 15T0-15T9. Potential on lead 13S91 is lowered because ring-up relay 7RU91 is operated and the corresponding tens identifier relay 15T9 pulls up. If two auxiliary line circuits are called at the same time it is necessary to restrict identification to only one of them. Preference is therefore given to the auxiliary line circuit with the lowest units digit. If only one line is being called the ringing current which is reapplied every 6 seconds causes the related units relay to re-operate during each cycle and reidentify the line. When, however, other calls are waiting to be identified they are given service in succession, the preference circuit for the units relays 5UO-5U9 being shifted each time. Trunk allotter. The operation of hold magnets 13H8, 13H9 also energizes 8H in start circuit 800. Accordingly 8HA pulls up to energize 11STA or 11STB depending on whether 11ST is operated or not and therefore on whether controller 1000 or 1400 is to be used. Assuming that controller 1000 is to be used 11STA energizes 11STA1 in controller connector 1100, energizes 17T in trunk allotter 1700, and operates 10P and restores 10PG in controller 1000. Operation of 17T provides for the seizure of an idle one of four trunks 16T1-16T4. If all four are available only one of relays 17TA0-17TA3 is operated and 17T energizes the next higher numbered one of 17TA1-17TA4. If a trunk is busy its related busy relay 17TB1-17TB4 is operated to shift the operating connection to the next higher one of 17TA1-17TA4. Assuming that 17TA1 operates it causes 16TS in trunk 16T1 to pull up. If the allotter cannot allot an available idle trunk due to a trouble condition, 6AA (not shown) pulls up slowly in the alternative allotter 600. If all four trunks are busy 6AA (not shown) is shunted before it can operate by energization of 17TC after the units digit has been pulsed to the terminating end, as described later. If allotter 600 is taken into use an alarm circuit is energized and the allotter 600 operates in the same manner as allotter 1700 except that all calls are served by trunk 16T1. Controller. In the absence of trouble conditions operation of 11STA operates 10P and restores 10PG in controller 1000, the armatures of polarized relays 10P, 10PG moving to the left and right, respectively. Operation of 11STA1 by 11STA extends the ring lead 16TR1 of trunk 16Tl through the lower windings of coils 16TC1, 16TC2, the winding of start relay 10ST1, and a break contact of 10ST2 to battery. As described later, the ring lead 16TR1 is connected over trunk 22T1 and the windings of relays 27PP and 27PN in controller 2700 to ground, the high resistance of the circuit preventing operation of 27PP and 27PN but allowing 10ST1 to operate. Pulsing units digit. 10ST1 energizes 10ST2 to initiate the operation of the pulse generator circuit. 10ST2 releases 10ST1 to operate 10W. 10ST2 also charges capacitor 10PGC and reverses current through IOP which moves its armature to the right or release position. Release of IOP, as described later, sends a pulse to the controller 2700, this pulse ending when capacitor 10PGC is fully charged so that 10PG pulls up and reoperates 10P. 10PG opens the conductive path to ring lead 10TR1 (not shown) and energizes 10X in series with 10W. 10PG also discharges 10PGC, to release 10PG and 10P to operate 10Y and the pulsing cycle is repeated with 10Z operating in series with 10Y at its conclusion. When 10PG again releases 10P releases to provide the third pulse and 10PU operates. When 10P re-operates to terminate the third pulse, relay 10ST2 releases to restore 10W-IOZ. When 10PG releases the pulse generator circuit also releases. Release of 10ST2 connects disconnect relay 10DC over the ring lead 16TR2 of the second trunk to disconnect relay 27DC in controller 2700. 10DC does not operate because of the high resistance but 27DC pulls up to disconnect the pulsing circuit over 16TR1 as a signal that the units digit has been received. Each release of 10P connects positive or negative sources 8CC1, 8CC2 through paths established by the sequential operation of 10W-10Z, under control of the units identifier 500 and relay 10DC1 to the ring lead 16TR1. The signal comprises one pulse with two spaces or three pulses which may be either positive or negative, according to a code. If more than one of the units relays 5U0-5U9 are operated the lowest is effective. Seizing allotted trunk. Operation of 10PU energizes 10PU1 to operate 17TC in the trunk allotter and 16S1 in trunk 16T1 as a seizure signal. 10PUI also restores the ring up relay, 7RU91 in the example, in the auxiliary line circuit to release the related units relay 5U1 and associated units indicating apparatus. The auxiliary line circuits are connected 30 to the first, 20 to the second, 30 to the third, and 20 to the fourth verticals of the trunk connector 900. As a